It is known to employ oil-separation and re-use systems operating in the high-pressure side of refrigeration apparatuses, e.g. U.S. Pat. Nos. 1,195,162, 1,254,519, 1,824,699, 2,002,033, 2,787,136, and 3,618,337. But none is known for operation in the low-pressure side of an ammonia system, where convenience and efficiency (nearly 100%) are higher.